When a patient suffers from acute or transient ischemia, oxygenation and delivery of blood to ischemic and postischemic tissue and/or organ sites is desired in order to prevent or minimize damage to the tissue and/or organ sites. For example, when a patient suffers from an acute myocardial infarction or a heart attack, support of the myocardium during or immediately following the infarction is desired. During a heart attack, the coronary arteries fail to provide adequate blood flow to the heart muscle. If the lack of a supply of oxygenated blood to the heart muscle continues for a prolonged period of time, irreversible damage to the heart can result.
In addition, many patients suffer reperfusion injury, i.e. slow coronary reflow or "no reflow", following successful angioplasty of occlusions responsible for an acute myocardial infarction or myocardial ischemia. To prevent or minimize reperfusion injury, hyperoxemic blood may be actively perfused into the coronary artery to improve blood flow with increased intracoronary pressure. In addition, the high level of oxygenation in the blood should improve oxygen delivery when diffusional distances between capillaries with normal blood flow are large. Finally, the compensatory hypercontractility of the normally perfused left ventricular segments may also benefit from an increase in oxygen supply.
Furthermore, during percutaneous transluminal coronary angioplasty (PTCA), the balloon inflation time is limited by the patient's tolerance to ischemia caused by the balloon inflation. Certain patients are especially at risk of ischemia because of the location or type of lesion, the amount of myocardium at risk, or poor left ventricular function, thereby limiting the performance of effective PTCA. Thus, active perfusion of hyperoxemic blood during PTCA is desired to lessen ischemia and to protect and support the myocardium during balloon inflation and to prolong the tolerated inflation time. Active perfusion of hyperoxemic blood after PTCA may also be desired to accelerate reversal of ischemia and/or recovery of myocardial function.
Conventional membrane or microporous hollow fiber oxygenators have been utilized to oxygenate blood in extracorporeal circuits. In these devices blood is withdrawn from a patient and by circulating the blood through the conventional oxygenator, the blood is oxygenated and delivered back to the patient.
Several disadvantages are associated with use of a conventional oxygenator to directly oxygenate blood. For example, the oxygenator requires a significant priming volume of blood, i.e. the volume of extracorporeal blood within the oxygenator for preparation of oxygen enriched blood. Because more than one quart of priming volume of extracorporeal blood is needed for an adult patient when using the conventional membrane oxygenator, a heat exchanger is usually necessary to maintain the temperature of the blood and a blood transfusion is also frequently necessary. Moreover, due to the large blood membrane oxygenator surface contact area and a relatively slow blood flow rate within the oxygenator, inflammatory cell reactions may be provoked and, in addition, a relatively aggressive anticoagulation therapy such as systemic heparinization may be necessary. Due to the large priming volume of the oxygenator, the oxygenator cannot be easily turned on and off because of the difficulties in flushing the blood from the system with saline and, upon cessation of flow, stagnant blood would result in thrombus formation. Additionally, the large priming volume increases the amount of blood at risk of thrombi formation, especially when stopping and starting the oxygenation. Furthermore, the use of conventional oxygenators to oxygenate blood involves high costs associated with the replacement of the oxygenator for each use. Finally, the maximum partial pressure of oxygen that can be achieved in blood with a conventional oxygenator is 1 bar. As a result of the challenges in using the conventional oxygenators, treatment of regional organ ischemia with conventional oxygenators has not been developed clinically.
With direct intravascular infusion of an oxygen supersaturated physiologic infusate into the blood stream, optimal mixing of the infusate with the blood may be difficult to obtain. For example, inadequate mixing of the infusate with blood may result in dangerous microbubble formation, and direct intravascular infusion would thus require the use of sensors to monitor the intravascular oxygen levels and to detect the intravascular presence of microbubbles.
Accordingly, there remains a need in the art for a safe, simple, efficient and cost-effective system and method for oxygenating a patient's blood by withdrawing and mixing the blood with an oxygen supersaturated physiologic infusate which provides for near physiologic flow rates within the system and which does not require a high priming volume of blood, a heat exchanger or aggressive systemic anticoagulation therapy.
There remains a further need in the art for a system and method for mixing and infusing a patient's blood and oxygen supersaturated physiologic infusate to a tissue or organ site of interest which provides adequate mixing of the infusate with the blood and which provides oxygenation of the blood at a target level.
There remains yet a further need in the art for a system and method for producing and delivering oxygen-supersaturated blood to a tissue or organ site of interest without bubble nucleation or growth during mixing of the nfusate with the blood or during infusion in the blood stream.